Piezo-crystal device



Sept. 2, 1941.

M. KLEIN I 2,254,371 PIEZO-CRYSTAL DEVICE Filed July 18, 1940 INVENTOR Patented Sept. 2, 1941 UNITED STATES. P T; OF

P IEZO-CRYSTAL DEYI CE Mark Klein, Flushing, N. Y., assignor to Premier Crystal Laboratories,-1nc.,- New York, N. Y., a

corporation of New York Application July is, 1940', Serial No. 346,101

' 12 Claims, (01. 171-327) This invention relates to piezo-crystal devices and more especially to holder and electrode arrangements for such devices.

A principal object is to provide an improved form of holder for piezo-crystals, especially those designed for low frequency Work. I

Another object is to provide an improved form of holder and electrode arrangement for piezo crystals of the clamped or contact type.

A further object relates to an improved form of electrode retainer for piezo crystals.

- A still further object is to provide an improved housing for a piezo crystal consisting of a ceramic annular member having ground edges and closed off at opposite ends by flat metal plates having ground surfaces. As a result the housing can be filledwith a gas under pressure since the abutting ground surfaces provide an effective seal against escape of the gas.

- A feature of the invention relates to a holder for piezo crystals of the contact or clamped type wherein one of the electrodes is rockably supported whereby it can automatically adapt itself to the surface of the crystal.

' Another feature relates to a holder for a piezo crystal of the contact or clamped type wherein pressure on the clamping electrode can be adjusted without changing the abutting facial relations between the electrode and the crystal.

" Another feature relates to improved means for retaining a rectangular or cornered crystal against sliding movement whileproviding means for adjustingand limiting the vertical movement of the crystal. j

Afurther feature relates to a simplified and readily assembled contacting arrangement between a piezo crystal and a rigid contact prong or plug.

A further feature relates to an improved manner of locking an adjustable piezo-electrode against unauthorized change of adjustment.

A further feature relates to a piezo crystal holder of the tri-part type wherein a pair of diametrically opposed contact prongs are provided, one of whichis readily removable and acts as a seal to close the exhaust or gas fillingopening leading into the cavity of the holder.

A still further feature relates .tothe novel organization, arrangement, relative location and interconnection of parts whereby there is produced a simple, accurate and easilyassembled piezo crystal holder of the gas-filled type.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

,In the drawing which illustrates one preferred embodiment of the invention,

Fig. 1 is a top plan view of a crystal and holder according to the invention.

Fig. 2 is a sectional view of Fig. 1 taken along line 22 and viewed in the direction of the arrows.

Fig. 3 is a sectional view of Fig. 2 taken along the line 3-3 and viewed inthe direction of the arrows.

Fig. 4 is a right-angle sectional view of Fig. 3 taken along the line 4-4.

Fig. 5 is an-enlarged view of part of Fig. 2.

The crystal housing according to the invention is formed in general of three members I, 2 and 3. -Members I and 2 are preferably of a corrosion resistant lightweight metal such as duralumin, Monel metal or the like. Member 3 is of a ceramic such as Isolantite or steatite which is capable of being accurately machined or ground for the purpose to be described. Members I and 2 act as cover plates for member 3 and are of the same peripheral shape and dimensions as member 3. Thus member 3 may be cylindrical and memhers I and 2 are therefore circular and with the same outside diameter as member 3 so that when the three members are assembled as shown in Fig. 2- the outside peripheral surface of the assembly is-perfectly smooth. The flat faces of member 3 which lap or butt against the corresponding flat faces of members I and 2, are all ground or machined with precision so that when assembled the 5. said faces form inthemselves a practical gastight seal.

-Member 3 is provided with a series of openings 4 to receive thescrews 5 by which member 2 is fastened to member 3. Member 3 is also provided with aseries of threaded openings to receive the screws 6 which fasten member I to member 3. In addition member 3 has a transverse threaded opening 1 into which is threaded the contact plug or'prong 8. The opening 1 is used to enable the housing to be evacuated and filled with an inert gas under pressure. The member 8 therefore serves not only as a contact prong but as a sealing or closure member for the housing. Member 3 is also provided with an opening 9 which communicates with opening "I, and member I has a recess l0 adapted to register with opening 9. A coiled compression spring l l is seated in opening 9 so that one end engages the threaded end of prong8 while the other end extends above the face of member 3 and into recess l0. Consequently when member I is tightly fastened against member 3 by screws 6, the spring II is compressed and insures good electrical contact between members I and 8. At the same time the end turn of spring I I enters a thread in the end of member 8 and provides protection against loosening of the prong 8 by vibration, jarring or the like. A prong I2 similar to prong 8 is threaded into the member 2 thus making electrical contact with the under face of the crystal.

In accordance with the invention the member 2 in addition to acting as a sealed closure for the housing, also serves as one of the electrodes which contacts the piezo crystal I3. As shown in Fig. 2 the crystal is of the low frequency type in which its thickness is a substantial fraction of its mass and while the drawing shows a rectangular or square cut crystal, it will be understood that other shapes or cuts can be used. In order to prevent the crystal sliding on electrade 2, there is fastened to the latter by screws I4, a metal ring I5 of brass, duralumin or other metal which is relatively soft as compared with the crystal. Ring I5 has a series of very shallow notches in its inner edge into which the corner portions of the crystal are received preferably with a snug fit. The upper electrode I6 of aluminum, duralumin or similar metal is circular and extends beyond the crystal edges except at the corners as shown more clearly in Fig. 3. Electrode I6 has its lower or crystal contacting face machined or ground to a perfectly flat smooth surface. The upper face of electrode I6 has a circular recess I"! to receive the pressure adjusting and clamping member I8. Member I8 is circular in cross section and has a slightly smaller outside diameter than the inside diameter of recess II so that electrode I6 is capable of limited tilting or rocking motion all directions with respect to the axis of member I8. For this purpose the lower or pressure end of member I8 is provided with a tapered portion I9 (Fig. 5) terminating in a flattened or slightly rounded tip I9. Preferably the fiat 20 on tip I9 is small as compared with the diameter of member I8.

The upper end of member It has a threaded rim 2I which engages a corresponding internal thread in a circular central opening in member I The upper face of member I8 has a slot 22 to receive a screw driver for adjusting the member I8 and thus limiting the movement of electrode IS with respect to the crystal. In order to prevent accidental or unauthorized change in the pressure adjustment, there is provided a guard or locking disc 23 which is threaded into the member I, Guard disc 23 has a hexagonal or other specially shaped hole 24 so that a special tool is required to loosen it. Disc 23 may be of the same metal as member I and in conjunction with rim 2| it serves to keep the housing gcstight. In the normal use of the device, electrode I6 rests on crystal I3 but there is a slight clearance of approximately 0.001 inch between the end 28 of member I8 and the bottom of recess H. The electrode I6 is therefore in contact with the crystal by reason of the weight of the electrode but its movement with respect to the crystal is limited. If desired the arrangement may be used so that the member I8 exerts a pressure on electrode I6 50 that the latter is lightly clamped against the crystal.

In order to make a positive electrical contact between member I and electrode I6 there is provided a flexible wire conductor 25 which is fastened at one end by screw 26 to electrode I6, and at the other end by screw 21 to member I.

From the foregoing it will be seen that the assembly of the device is very easily accomplished, the crystal being placed in the ring I5, after which the member I together with the electrode I6 is placed in position with the spring II set into recess I0. If desired the member I8 may be threaded into member I prior to assembly of the latter in place so that the end of member I8 holds electrode I6 in place while the screws 6 are being tightened. The cavity of the assembled housing is then evacuated and provided with a filling of an inert gas such as neon or nitrogen under pressure whereupon the prong 8 is fastened in place to prevent the escape of gas. The member I8 may then be adjusted to provide the requisite clearance between end 28 and bottom of recess I! or to adjust the clamping pressure on the crytal in the event a clamping action is desired, whereupon the guard disc 23 may be tightened. Because of the relative mechanical independence of the member I8 and the electrode I6, if for any reason the upper face of crystal I3 is not exactly parallel to the under face, the electrode I6 rests on and therefore automatically adapts itself to the surface of the crystal. Furthermore this surface contact between the upper face of the crystal and the under face of electrode I6 is not disturbed even though the member I8 is turned for adjustment. Heretofore where the upper electrode is made integral with the adjusting shank, the very fact that the latter is adjusted by a helically threaded screw action precludes the maintenance of a uniform opposing surface relation between the lower face of the upper electrode and the upper face of the crystal consequently the spacing is most likely to be greater at one side of the crystal than at the other. Furthermore if for any reason there is any surface irregularity in the upper or lower faces of the crystal there is less chance of the crystal being cracked by the clamping pressure with the arrangement shown, since the clamping forces are substantially uniformly distributed over the crystal faces.

While certain specific materials and shapes have been mentioned herein, it will be understood that the same are merely illustrative and that various changes and modifications can be made Without departing from the spirit and scope of the invention. Thus if desired the outer peripheral surface of the assembled members I, 2 and 3 may be given a coat of lacquer or waterproof varnish. While in the foregoing reference has been made to a gas under pressure, it will be understood that the pressure may be approximately atmospheric pressure or at a much higher pressure than atmospheric pressure.

What I claim is:

1. A piezo crystal device comprising a pair of electrodes between which a crystal is positioned, one of said electrodes being movable with respect to the other, and means to limit the movement of said one electrode with relation to the crystal while allowing it to adapt itself to the surface of said crystal.

2. A piezo crystal device comprising a pair of electrodes between which a crystal is positioned, one of said electrodes resting on the crystal and having limited freedom of movement with respect to the other electrode, and adjustable means to limit the movement of said one electrode with respect to the crystal.

3. A piezo crystal device comprising a housing having a pair of electrodes between which a crystal is held, means to adjust the position of one of said electrodes with relation to a face of the crystal, the last-mentioned means comprising an adjustable abutment threaded through a wall of said housing, and a recess in one face of said electrode to receive loosely the end of said abutment.

4. A piezo crystal device according to claim 1 in which said abutment is, provided with a tapered end engaging said electrode to enable said electrode to assume a tilted position with respect to the axis of said abutment.

5. A piezo crystal device according to claim 1 in which said electrode is electrically connected to said housing wall by a flexible conductor.

6. A piezo crystal device comprising a housing having a pair of electrodes between which a crystal is held, an adjustable abutment carried by one wall of said housing and projecting interiorly thereof, a recess in a face of one of said electrodes and having peripheral dimensions slightly greater than those of the abutment, the end of said abutment being slightly spaced from the bottom of said recess to allow said electrode to have a limited tilting movement with respect to said abutment.

7. A device according to claim 6, in which said abutment is adjustably threaded through said housing wall whereby the spacing between said abutment and electrode can be adjusted without varying the surface relations between said electrode and crystal.

8. A piezo crystal device comprising a pair of electrodes one of which is adjustable, a crystal between said electrodes, a threaded adjustment member the end of said member being in engagement with said electrode so that it can limit the movement of said electrode while allowing substantial universal movement of said electrode with respect to the axis of said threaded member.

9. A device according to claim 8 in which said electrode is capable of limited universal tilting motion with respect to the axis of said adjusting member.

10. A piezo crystal device comprising a tri-part housing consisting of a central annular section of insulating material, end closure plates of metal removably fastened to said annular section, a contact plug fastened to one closure plate, a contact plug fastened into said annular section, a passage in the wall of said annular section communicating with said plug, a spring seated in said passage and arranged to resiliently contact said other closure plate and to be compressed by the fastening of said other closure plate, and a flexible conductor connecting said electrode to said other closure plate.

11. A piezo crystal device according to claim 10 in which the second-mentioned contact plug is threaded through a gas filling opening in the wall of said annular insulating section said plug having its threaded end engaged by said spring.

12. A piezo crystal device comprising a tri-part housing consisting of a central hollow section of ceramic having ground flat end walls, metal end closure plates having flat smooth faces in gastight relation and sealing contact with said end walls, a crystal resting on one of said closure plates, an adjusting member carried by the other of said closure plates, a filling of inert gas within said housing, a crystal retaining ring removably attached to the inner face of said one of said closure plates, said ring having indentations in its edge to receive the corners of said crystal.

MARK KLEIN. 

